diff --git a/src/acl.c b/src/acl.c
index 7666616..9ab643e 100644
--- a/src/acl.c
+++ b/src/acl.c
@@ -72,7 +72,7 @@ static vector_t access_list = NULL;
  */
 static int
 fill_netmask_array (char *bitmask_string, unsigned char array[],
-                    ssize_t len)
+                    size_t len)
 {
         unsigned int i;
         long int mask;